Producing alpha cellulsoe from cottonseed hull fibers



Patented Jan. 2, 1951 OFFICE PRODUCING ALPHA CELLULO SE FROM 4 COTTONSEED HULL FIBERS Jefferson L. Eskridge, Long Island City, N. Y.

No Drawing. Application July 17, 1945, Serial No. 605,639

12 Claims.

The present case is a continuation-in-part of my copending application Serial No. 324,623 (filed March 18, 1940, which is now abandoned).

This invention relates to an improved process for recovering comparatively high grade alpha cellulose from a comparatively low grade and cheap cellulose-containing material namely cotton seed hull fibre.

Heretofore alpha cellulose has commonly been made from cotton linters. However, cotton seed hull fibre which material, as well known, is obtained from cotton seed hulls after the removal of the linters, is lower in cost than linters and while attempts have been made to utilize such hull fibre, the yield and grade of cellulose so made and cost of processing (by the processes known before my present invention) have been such that previous processes have not been commercially satisfactory. Prior to 1941, the U. S. Navy Department would not accept cellulose (for nitration) made from hull fibre nor cellulose made from mixtures of linters and hull fibre.

According to the present invention, cotton seed hull fibre may be treated to liberate the cellulose thereof in such a manner that the cellulose will have a high alpha cellulose content while still obtaining a high yield. The method of processing is such that excellent results are obtained with a very low cost material and processing cost so that the process is commercially practicable.

The method is also adapted for the purification and improvement in grade of other cellulosic material than hull fibre, i. e. linters of all grades can be treated by the present process, and high alpha cellulose can thereby be made from such linters. From any given grade of linters, the present process gives a better grade of alpha cellulose than the processes heretofore used.

A further object of the present invention resides in the provision of alpha cellulose having new and novel characteristics, particularly alpha cellulose pulp having a lower copper number and a lower ash content than now attainable from any source (and far lower than those of any alpha cellulose heretofore made from hull fibres).

In general the improved process may be considered as a two-step process. First, there is a digesting or cooking step to liberate the cellulose, and this may be followed by a bleaching step of any suitable kind. The novelty in the present invention is in the digestion step. For more completely explaining the present invention, the following examples are given:

Example 1.---Materials used in the digesting step were in the following amounts per ton of air-dry hull fibre:

12,000 lbs. of softened water 200 lbs. of sodium hydroxide 8 lbs. of ammonium hydroxide (26 B.) 12 lbs. of potassium carbonate 4 lbs. of ammonium oxalate Expressed as percentage ratios based on airdry weight of raw material, i. e. cotton seed hull fibre, the ratios are as follows:

100.0 parts of air-dry hull fibre 600.0 parts of water 10.0 parts of sodium hydroxide 0.417 parts of ammonium hydroxide (26 B.) 0.625 parts of potassium carbonate 0.2085 parts of ammonium oxalate In this example, the percentage of NaOH in the digestive solution was about 1.636, and total chemicals in the liquor amounted to about 1.84

A particular experimental run of the process was as follows: A suitable quantity of cotton seed hull fibre, for example, lbs. on an air-dry basis (moisturecontent about 9.5%) was charged into a suitable digester, e. g. of the tumbling type with a jacket, together with the proportionate amounts of the above chemicals and water according to the foregoing formula. After sealing the digester, superheated steam was admitted to the jacket of the digester and the contents cooked or digested by indirect heating, while agitating, by rotating the digester. After heating for a period of 1% hours, the temperature of the cook had reached C. The pressure within the digester at this temperature was then about 109 lbs. In cooking, it is preferable to use heating by indirect steam to avoid possible iron contamination. While some difliculty was found in maintaining a uniform cooking temperature of just 160 C., during the run, it was found that the temperature could be maintained within a range of i 4 C., i. e. between 156 and 164 C. During cooking the pressure gauge reading varied from a maximum of 119 lbs. to a minimum of 92 lbs. After reaching the cooking temperature of 160 C. cooking was continued for a further period of 2 hours at approximately such temperature of 160 C. After cooking for such further period, the relief valve was opened somewhat, and the steam supply to the jacket was cut off and the pressure in the digester was allowed to go down to 50 lbs., and thereafter the digester charge was blown out of the digester into a blow pit. In such moisture samples was 83.8 percent, based on the hull fibre (dry basis). After the yield had been determined, the pulp was removed from the blow pit and washed in a beater with the beating roll in raised position. The fines removed from the pulp amounted to approximately 0.72 percent of the total pulp. This figure was determined by weighing one beater charge before and after washing and from the observed loss, calculating the amount of fines in the entire cook;

The pulp was thereafter bleached, using a hypochlorite solution followed by S02.

SUMMARY OF YIELDS AND CHEMICAL rns'rs Tests on unbleached pulp Total pulp yield (approximate), perure reported is slightly lower than it should actually be. The yield as determined by triplicate amount of the caustic soda. Here the amount of caustic soda is 10% of the amount of the hull fibre. The water to hull fibre ratio in this example is 6:1.

For getting best results, I do not depart very greatly from the ratio of 1 ammonium oxalate, 2 ammonium hydroxide (calculated as 26 B.) 3 potassium carbonate to 48 of caustic soda. Some variation from these figures (up to a variation of 33% in either direction, above or below) is permissible'and is included within, the scope of the invention.

; Caustic soda solution alone, of the concentrations here set forth, and at high temperatures (at the boiling point under pressure) is well known to cause degrading of the celluloses. The ammonium hydroxide, potassium carbonate, and ammonium oxalate, added in about the proportions above indicated, together act to inhibit such degrading of the cellulose. I do not attempt to explain why such agents acts as inhibitors of degrading, but content myself with stating the observed results.

While I have given above the ingredients and relative proportions of ingredients to obtain good yields of pulp with-desirable characteristics, it will be apparent to those skilled in the art that the proportions and amounts ,of chemicals to be used may in some instances be varied. depending upon the kind, quality, condition and cent 83.8 t 1 ate)), ercent 0.72 S or Source of pp y of the raw hull fibre $3 2 5? ggiggfg fifig fi; 832 or linters available for treatment and results de- A1pha cenu1ose (unbleached) percent sired. In practice and based upon tests and (based on accepted pulp) 97.83 experiments which I v ade, the proportions Ash (unbleached), percent 0.62 and ingredients digesting and cooking hull Iron in ash (unbleached), percent 6.8 fibres lint y y as ows and I on in pulp, P. P. M. (unbleached) 41.3 yet afford the most advantageous results in the Copper in pulp, percent 0.0005 described process.

Per Cent on Air- I P d T g g gggg as was Sodium hydroxide (or equal strength mixed sodium hydroxide and 8% to 12% 160 to 240 lbs.

sodium carbonate). Water 500%to1200% 10,000 to 24,000 lbs. Ammonium hydroxide, 26 B 55% to 5% 6% to 10 lbs. Potassium carbonate. 98% ca c to 54% 10 to 15 lbs. Ammonium oxalate (cryst- 0. p.) 56% to 54% 3% to 5 lbs.

Calcium in pulp, percent Silica in pulp, percent Viscosity (in 1% cuprammonium solution) centipoises 33 to 34.0

Tests on bleached pulp Brightness, percent 79.6

Alpha-cellulose, percent 97.82 Cuprammonium viscosity, centipoises 21.5 Copper number 0.12 Pentosans, percent 0.47 Ether solubility, percent 0.06 NaOH solubility (7.14%), percent 3.61

Ash, percent 0.030

Iron in ash, percent 7.1 Iron in pulp, P. P. M 21.3 Copper in pulp, P. P. M 5.0 Calcium in pulp, P. P. M Silica in pulp, P. P. M 148 The cellulose. pulp produced by Example 1 was very suitable (after bleaching) for making nitrocellulose for use in explosives. When it is desired to make cellulose pulp suitable for acetylation (e. g. for the production of threads, films, etc.), it is preferable to somewhat modify the process, to give a grade of pulp of substantially the same purity but much higher viscosity, and this result can be accomplished by somewhat increasing the amount of the digestive liquor (per ton of the hull fibre used) somewhat decreasing the concentration of said liquor and/or somewhat decreasing the temperature and pressure in the cooking treatment. The cellulose prepared by Example 1 has a viscosity of about 33-34 cps., and is very suitable for nitration for use in the production of smokeless powder.

While I have above described a very preferred embodiment, I do not confine the invention to this example. The ratio of water to hull fibre (6: 1 in the above example) may vary between 5:1

and 12:1, the other factors being adjusted accordingly. The amount of caustic soda based on the hull fibre, which is 10% in the above example, may vary between 5% and 25%. It will be understood that when larger amounts than 10% are used, the temperature and pressure of the cookingshould be lower, and the time of cooking should be shortened.

For cellulose for nitration purposes, I prefer to adjust the cooking to give a relatively low will usually give cellulose of higher viscosity.

w p i c 11 :1 80 2% 200 270 to 323 :1 60 2 200 342 9:1 00 2 200 432 7:1 75 2 200 100 7.5:1 75 2 200 Z30 10:1 100 2% 200 100 7:1 100 2% 200 47 7:1 100 3 120 8:1 70 1 300 9:1 60 l 400 Acosptable (or nitration.

In' the last table above given, the digestive liquors contained (when fresh) of caustic soda, respectively about 1.1%, 0.988%, 1.1%, 1.4%, 1.313%. 0.98%, 1.4%, 0.85%, 1.85% and 2.17%. The total chemicals in said liquors represented respectively about 1.23%, 1.11%, 1.23%, 1.58%, 1.48%, 1.11%, 1.58%, 0.955%, 2.07% and 2.44%. In Example 1, given above,these figures are respectively 1.636% and 1.84%.

In all of the above tests, a mixture of 1 part ammonium oxalate, 2 parts ammonium hydroxide (figured as 26 B.), and 3 parts potassium carbonate, approximately equal to one-eighth of the amount 01' caustic soda was added to the cooking liquor. The pressure being stated, it is not necessary tostate the temperature, the liquor being kept at close to the boiling point for the existing pressure, throughout the period of cookin 7 From the last table above, it will be observed that the liquors here used contain from about 0.955% to about 2.44% of dissolved chemicals, this table being given by way of example, and not by way of limitation.

Except as stated, the process of treatment in these cooks followed Example 1, given above.

I have above shown the amount of theinhibitors of degrading of the cellulose (ammonium hydroxide, ammonium oxalate and potassium car bonate, together) as being equal to one-eighth of the amountof caustic soda. For best results, I recommended keeping the combined amounts of these inhibitors at well within the limits onetenth to one-sixth of the amount of caustic soda.

While I prefer caustic soda, NaOH, as the main alkali in the cooking liquor, this in contact with air may be partly converted into iodiuhi carbonate. Also recaustization of recovered soda in the process may leave some sodium carbonate present. The cooking liquor accordingly may contain both caustic and carbonate, and these are both active and are included under the name caustic soda. It is noted that the commercial grades of caustic soda usually contain some sodium carbonate.

I claim:

1. In the treatment of a raw material containing cotton seed hull fibre as a substantial constituent, by digestion under a superatmospheric pressure of about 60 lbs. to about 119 lbs. per square inch, with a caustic soda solution of a concentration which it used alone would be liable to cause degradation of the cellulose in said fibre, namely the concentration of caustic soda in said solution being between about 0.85% and about 2.17%. such digestion being conducted at approximately the boiling point of such solution under the existing pressure, the. improvement which comprises adding to said solution, before said digestion step, an agent for preventing such degradation, to some extent at least, said agent being a mixture of 1 part ammonium oxalate, ammonia water equivalent to about 2 parts of 26 B. ammonium hydroxide and about 3 parts potassium carbonate, the amount of said agent being between one-tenth and one-sixth or the amount of said caustic soda, and such digestion being continued for about 1 hour to about 3 hours.

2. A process of obtaining alpha cellulose from cotton seed hull fibres, comprising digesting the fibres substantially free from visible pieces of cotton seed hull of substantial side, underabout 109 pounds superatmospheric pressure and at a temperature of about C. in a digesting solution which consists essentially of the following inmdients expressed in percentage ratios with respect to the amount of air-dry hull fibre used:

about 600.0% water I about 10.0% caustic soda I about 0.417% ammonium hydroxide (26 as.)

about 0.625% potassium carbonate about 020.85% ammonium oxalate said digestion being continued for about i to 3 hours and until the hull fibre is sufficiently ioosand cotton linters, which comprises cooking such cellulosic material substantially free from visible pieces of cotton seed hull of substantial size, in

from 5 to 12 times its weight of water containing as the essential digestive, agents, the following chemicals in the proportions stated:

Parts ammonium oxalate about 1 ammonium hydroxide 26 B about 2 potassium carbonate-.. about 3 caustic soda about 48 the amount of such caustic soda being between 6% and 20% of the amount of such cellulosic material, and said cooking liquor containing about 0.955% toabout 2.44% of said four dissolved chemicals, and the cooking operation being conducted under a superatmospheric pressure 15 of about 60 to about 119 pounds per square inch and at about the boiling point or the liquor under the existing pressure, said digestion being continued for 1 to 3 hours and until the said cellulosic material is sufiiciently loosened to be capable separation into individual fibres by beating, and when using over 10% of caustic soda, relative to the hull fibre, selecting temperature, pressure and time factors in the lower part of the above stated ranges.

4. A process or making cellulose of high alpha content which comprises cooking a cellulosic material which contains the fuzz of cotton seed hull, in an aqueous solution containing caustic soda in such a concentration that if used alone it would have a. degrading action on alpha cellulose, and an agent for inhibiting the degrading action of caustic soda on alpha cellulose, said inhibiting agent being a mixture of 1 part oi ammonium oxalate, about 2 parts of ammonium hydroxide calculated as 26 B. ammonia water and about 3 parts of potassium carbonate, and the amount of such inhibiting agent being between and V 0! the amount 01' such caustic soda, the caustic soda in said solution being between about 10% and about 25% of the amount of such cellulosic material, and the water in such solution being between about 5 and about 12 times the amount of such cellulosic material, and the percentage 0! caustic soda in said aqueous solution being between 0.85 and 2.17, and the cooking being carried out at a temperature of at least 156 C., in a closed vessel under a superatmospheric pressure of about 60 lbs. to about 119 lbs. per square inch above atmospheric, and'being continued for about 1 hour to about 3 hours, and when using over of caustic soda, relative to said cellulosic material, selecting temperature, pressure and time factors in the lower part of the above stated ranges.

5. A process of producing cellulose of high alpha content which comprises cooking a cellulosic material substantially free from visible pieces of cotton seed hull of substantial size, selected from the group consisting of cotton seed hull fibre and linters, in an aqueous digestive solution which consists essentially of dissolved caustic soda and an agent for inhibiting the degradation oi alpha cellulose by said caustic soda, said digestive solution containing between 0.85% and 2.17% of dissolved caustic soda, and said agent for inhibiting degradation being a mixture of about 1 part ammonium oxalate, about 2 parts ammonium hydroxide calculated as 26 B. ammonia water and about 3 parts potassium carbonate, the combined amounts of said three last mentioned substances being between one-tenth and one-sixth of the amount 01' said caustic soda in such solution, the amount of caustic soda being between 6% and of the amount of said cellulosic material and the amount of water being between 500% and 1200% of the amount of said cellulosic material, said cooking being conducted under 60 to 119 pounds superatmospheric pressure and at approximately the boiling point of the liquor under the existing superatmospheric pressure, and continuing said cooking operation for about one hour to about three hours, and when using over 10% of caustic soda, relative to said cellulosic material, selecting temperature, pressure and time factors in the lower part of the above stated ranges.

6. A process of making alpha cellulose which comprises digesting cotton seed hull fiber at aboutthe boiling point oi the solution, in a digestive solution which consists essentially, per ton of ing in solution about 200 lbs. of caustic soda and an agent to prevent degradation of the alpha cellulose, for about 2 to 2.5 hours, under a superatmospheric pressure of about lbs., the agent for preventing degradation, being 1 part ammonium oxalate, about 2 parts ammonia water calculated as 26 B. solution and about 3 parts oi. potassium carbonate, and the amount oi. such agenttor preventing degradation being between lio and V6 oi the amountbi such caustic soda.

7. A process of making alpha cellulose which comprises digesting cotton seed hull fiber at about the boiling point of the solution, in a digestive solution which consists essentially, per ton of such fiber, of about 7 to 7.5 tons of water containing in solution about 200 lbs. of caustic soda an agent for preventing degradation of alpha cellulose for about 2.5 hours, under a superstmospheric pressure of about to lbs., the agent for preventing degradation of the cellulose being 1 part of ammonium oxalate, about 2 parts of ammonia water calculated as 26 B. solution and about 3 parts of potassium carbonate, and the amount 01 such agent for preventing degradation being between ti and V; of the amount of such caustic soda.

8. A process of making alpha cellulose which comprises digesting cotton seed hull fiber at about the boiling point of the solution, in a digestive solution, which consists essentially, per ton of such fiber, of about 7 tons of water containing in solution about lbs. of caustic soda and an agent for preventing degradation oi the alpha cellulose, for about 3 hours under a superatmospheric pressure of about 100 lbs. the agent for preventing degradation of the cellulose being 1 part of ammonium oxalate, about 2 parts of ammonia water calculated as 26 B. solution and about 3 parts of potassium carbonate, and the amount 01' such agent for preventing degradation being between M and V6 oi the amount of such caustic soda.

9. A process of making alpha cellulose which comprises digesting cotton seed hull fiber at about the boiling point of the solution, in a digestive solution which consists essentially, per ton of such fiber, of about 10 tons of water containing in solution about 200 lbs. of caustic soda and an agent to prevent degradation oi the alpha cellulose, for about 2.5 hours. under a superatmospheric pressure oi about 100 lbs., the agent for preventing degradation being 1 part ammonium oxalate, about 2 parts of ammonia water calculated as 26 B. solution and about 3 parts of potassium carbonate, and the amount of such agent for preventing degradation being between 94 and Va 0! the amount of such caustic soda.

10. A process of making alpha cellulose which comprises digesting cotton seed hull fiber at about the boiling point of the solution, in a digestive solution which consists essentially, per ton of such fiber, 01' about 9 tons oi. water containing in solution about 400 lbs. of caustic soda and an agent to prevent degradation of the alpha cellulose, for about an hour, under a superatmospheric pressure of about 60 lbs., the agent for preventing degradation being 1 part ammonium oxalate, about 2 parts of ammonia water calculated as 26 B. solution and about 3 parts of potassium carbonate, and the amount of such agent for preventing degradation being between $5 and V. of the amount of such caustic soda.

11. As a new composition or matter, a digestive I solution suitable for cooking cotton seed hull masueh nben, 01 about 9 to 10 tons 0! water contain- 15 terial which is an aqueous solution which consists O essentially of water containin! in solution, the following:

Parts ammonium oxalate about 1 ammonium hydroxide calculated as 26 Be about 2 potassium carbonate about 3 caustic soda about 48 the caustic soda in the solution being between about 0.85% and about 2.17%, based on the total digestive solution.

12. As a new composition or matter, a digestive solution suitable for cooking fuzz of cotton seed hull, which is a solution in water, the essential dissolved constituents of which are ammonia oxalate, about 1 part ammonium hydroxide calculated as 36' 36.. about 2 parts 10 potassium carbonate, about 3 parts caustic soda from about 36 parts to about 60 the percentage of the caustic soda in such solu- 6 tion being between about 0.85 and about 2.17.

JEFFERSON L. ESKRIDGE.

REFERENCES CITED The following references are of record in the 10 tile 0! this patent:

UNITED STATES PATENTS 

1. IN THE TREATMENT OF A RAW MATERIAL CONTAINING COTTON SEED HULL FIBRE AS A SUBSTANTIAL CONSITUTENT, BY DIGESTION UNDER A SUPERATMOSPHERIC PRESSURE OF ABOUT 60 LBS. TO ABOUT 119 LBS. PER SQUARE INCH, WITH A CAUSTIC SODA SOLUTION OF A CONCENTRATION WHICH IF USED ALONE WOULD BE LIABLE TO CAUSE DEGRADATION OF THE CELLULOSE IN SAID FIBRE, NAMELY THE CONCENTRATION OF CAUSTIC SODA IN SAID SOLUTION BEING BETWEEN ABOUT 0.85% AND ABOUT 2.17%, SUCH DIGESTION BEING CONDUCTED AT APPROXIMATELY THE COILING POINT OF SUCH SOLUTION UNDER THE EXISTING PRESSURE, THE IMPROVEMENT WHICH COMPRISES ADDING TO SAID SOLUTION, BEFORE SAID DIGESTION STEP, AN AGENT FOR PREVENTING SUCH DEGRADATION, TO SOME EXTENT AT LEAST, SAID AGENT BEING A MIXTURE OF 1 PART AMMONIUM OXALATE, AMMONIA WATER EQUIVALENT TO ABOUT 2 PARTS OF 26* BE. AMMONIUM HYDROXIDE AND ABOUT 3 PARTS POTASSIUM CARBONATE, THE AMOUNT OF SAID AGENT BEING BETWEEN ONE-TENTH AND ONE-SIXTH OF THE AMOUNT OF SAID CAUSTIC SODA, AND SUCH DIGESTION BEING CONTINUED FOR ABOUT 1 HOUR TO ABOUT 3 HOURS. 